The present invention relates to a cleaning method and apparatus in which composite particles consisting of snowlike ice powder and snow-like dry ice are projected against an object to be cleaned.
There are two typical cleaning methods of this kind; that is, (1) sand blasting method in which sand is projected under high pressure through a nozzle against an object to be cleaned and (2) a dry-ice blasting method in which large lumps of dry ice are broken into finely divided particles and such dry-ice particles are projected against an object to be cleaned.
In the sand blasting method, dust or the like is scattered too much. Especially when the sand blasting method is employed for cleaning of various devices and equipment in a nuclear power plant, there arises a problem that dust including radioactive substances is scattered and discharged into the atmosphere.
In the dry-ice blasting method, when relatively large lumps of dry ice are broken into finely divided dry-ice particles, dry-ice particles tend to become powder. As a result, the yield of the dry ice used is poor and the dry-ice blasting method becomes very expensive. Furthermore, there is a problem that dry-ice particles are vaporized during the cleaning operation so that an object being cleaned cannot be seen. That is, the working conditions are adversely affected.
The present invention was made to overcome the above and other problems and has its primary object to project particles whose surfaces are harder than those of dry-ice particles, thereby improving the cleaning efficiency. To the above and other ends, according to the present invention, snow-like solids (to be called "snow dry ice") are produced from liquefied carbon dioxide and a liquid is sprayed over the snow dry ice, whereby the snow mixture consisting of dry ice and frozen liquid is produced. The snow mixture is compressed in the form of particles or chalk-like elongated pieces and charged into a projector so as to be projected against an object by compressed air or water under high pressure. The liquid is frozen over the surface of each dry-ice particles so that the surfaces of the composite particles become very hard so that the blasting efficiency can be improved. Furthermore the ice surfaces are broken when the composite particles strike against an object to be cleaned so that a wet type blasting can be carried out. As a result, the phenomenon that an object becomes invisible due to the vaporization of dry-ice particles can be avoided.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of a preferred embodiment of the present invention taken in conjunction with the accompanying drawings.